The present invention relates to basic refractory cementitious material and components thereof.
The invention moreover relates to a method of making such cementitious components as are exposed to chemical attack, wear and erosion by molten metals such as steel.
Refractory components of valves, and refractory nozzles for various purposes in the metal pouring art, having conventionally been produced by pressing and firing at high temperaturs. Costly, high purity materials such as zirconia and 85 to 95% Al.sub.2 O.sub.3 -based refractories have been considered necessary in view of the extremely harsh service conditions to which the components are subjected. Energy expended in producing components by pressing and firing is substantial, since firing temperatures normally exceeding 1500.degree. C. must be created and maintained throughout the firing process. The energy expenditure contributes significantly to the unit costs of components made from such fired refractory materials.
Despite the use of strong fired refractories in the metal pouring art, items such as valve plates commonly need frequent replacement at great cost.
Early prejudices against the use of refractory concretes--revolving around the belief that they could not possibly withstand harsh working conditions--are being overcome and concrete systems are being considered for the manufacture of metal pouring refractory components.
Recently, chemically-bonded concretes have been proposed, for instance for sliding gate valve plates. Like fired refractory plates, chemically bonded concrete plates are unlikely to withstand repeated thermal shocks. Thus, their use in valves for ingot teeming is expected to be beset by inconvenient stoppages for their replacement.
We have found certain hydraulically-bonded basic cementitious materials surprisingly possess the ability to withstand thermal shock extremely well, and the production of components from these materials is particularly straightforward. Our proposed materials are composed of magnesia and an hydraulic aluminous cement, and in addition free alumina, the latter being thought to contribute significantly to stabilizing and strengthening components made from our materials.